1. Field of the Invention
The present invention relates to an image recording apparatus which reduces deviation in the feeding distance or feeding speed of a recording material and the movement of a printing head.
2. Background Arts
Various printers such as an inkjet printer, a thermal printer and the like are generally used for recording an image on recording paper. When some malfunction occurs in a recording device of the printer, image quality of the recorded image becomes inferior. Taking a case of the inkjet printer, for example, a nozzle for ejecting ink is sometimes clogged with the ink. The clogging causes imperfection in ink ejection, since an ejection amount is decreased. Imperfection in ink ejection causes streaky color unevenness and density unevenness which appear on the recorded image.
When color unevenness or density unevenness happens, the printer is switched over a head cleaning mode to correct imperfection in ink ejection of the recording device. Since color unevenness or density unevenness causes waste of the ink and the recording paper, some business-use printers automatically print test patterns to correct imperfection in ink ejection at regular time intervals. (for example, United States Patent Publication No. 2001/0004284 and Japanese Patent Laid-Open Publication No. 11-198358.) U.S. Pat. No. 6,412,902 also discloses a printer which prints test patterns on a margin between images, in order to reduce the waste of recording paper.
The cleaning of the printing head, as described above, can correct print imperfection caused by the recording device. The streaky unevenness, however, still appears, since it is caused by deviation in the feeding distance of the recording paper and the movement of the printing head.
These days, various types of recording paper having different texture, thickness, width and the like have been used. The friction between the recording paper and a pair of feed rollers is changed depending on the type of recording paper, so that the feeding distance or feeding speed of the recording paper deviates. The friction between the recording paper and the feed roller pair slightly varies in accordance with the variation in environment temperature and humidity. The diameter of the feed roller also varies in accordance with the variation in environment temperature. Therefore, there is a problem that the deviation in the feeding distance or feeding speed of the recording paper causes a white streak appearing in an unprinted area, or a black streak appearing in an area where adjacent print lines are overlapped.